half equations in electrolysis?!

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in unit 2 gcse aqa chemistry and dont get them?!?! how do you form them and know how many numbers to put and stuff?! any help would be much apprechiated! thankyou very much:')

<3

Posted Thu 27th December, 2012 @ 12:36 by elllieeeeeeeee

5 Answers

  • 1 vote

thankyou tilly!!! that was such a good explaination!!! so you've only put 1 electron and sometimes i see there is more than one, how do you know how many?:)

thankyou!

<3

Answered Sat 29th December, 2012 @ 10:42 by elllieeeeeeeee
  • 1 vote

That's Ok : )

The number of electrons depends on the charge of the ions. 

Cl- has a charge of 1- so it only has 1 electron more than it should. so it only needs to lose 1. 

Na+ has a charge of 1+ so it only has 1 electron less than it should. So it only needs to gain 1. 

You have to look at the periodic table to know the charge of the ion. The charge will depend on the group it is in. 

So magnesium is in group 2, so it needs to gain 2 electrons, so it's half equation will be:

Mg2+ + 2e- => Mg

Answered Sat 29th December, 2012 @ 10:45 by Former Member
Edited by Former Member on Sat 29th December, 2012 @ 10:54
  • 0 votes

Basically half equations show what is happening  to the electrons. The whole point of electrolysis is to split up an ionic compound and turn the ions back into electrons. So you have to add and remove electrons to get atoms.

Half equations show how you get those atoms from the ions. 

Say you have NaCl, and so you get an aqeuous solution of Na+ ions and Cl- ions. The Na+ go to the negative electrode (cathode). So Na+ gains an electron to become Na.

The half equation is: Na+ + e- => Na

You also have Cl-. This is attratced to the positive electrode (anode). So Cl- loses an electron to become Cl.

The half equation is: Cl- => Cl + e-

Answered Fri 28th December, 2012 @ 19:38 by Former Member
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^that is brilliant tilly i didnt know that and it makes it all make sense now! thankyouuu so much!!

<3

Answered Mon 31st December, 2012 @ 13:10 by elllieeeeeeeee
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That's ok. Ask me if you need any more help! ; )

Answered Mon 31st December, 2012 @ 13:21 by Former Member